What does Two Bit mean when he says the only keeping darry from being a soc is us?

Two-Bit means that Darry's responsibilities and commitment to taking care of his younger brothers, Ponyboy and Sodapop, is the only thing keeping him from being more like the wealthy, privileged "Soc" group. Darry sacrifices his own desires and opportunities in order to provide for his family, which sets him apart from the typical Soc lifestyle.